Color filter for image sensor, image sensor, and method of manufacturing color filter for image sensor

ABSTRACT

Provided are: a color filter for an image sensor in which an infrared filter having no particulate defects or the like can be laminated adjacent to an image pickup element and in which the total thickness of an image sensor can be significantly reduced; an image sensor including the color filter for an image sensor; and a method of manufacturing the color filter for an image sensor. The color filter for an image sensor includes: two or more absorbing color filters that absorb light components having different wavelength ranges; and a cholesteric reflecting layer in which a right circularly polarized light cholesteric layer having right circularly polarized light reflecting properties and a left circularly polarized light cholesteric layer having left circularly polarized light reflecting properties are laminated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2017/022944 filed on Jun. 22, 2017, which claims priority under 35U.S.C. § 119(a) to Japanese Patent Application No. 2016-131980 filed onJul. 1, 2016 and Japanese Patent Application No. 2016-166834 filed onAug. 29, 2016. Each of the above applications is hereby expresslyincorporated by reference, in its entirety, into the presentapplication.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a color filter for an image sensor usedfor an image sensor, an image sensor including this color filter for animage sensor, and a method of manufacturing the color filter for animage sensor.

2. Description of the Related Art

Recently, various image sensors including a solid image pickup elementsuch as photodiode are used.

In order to obtain a color image using an image sensor, in general,color filters of three primary colors including red (R), green (G), andblue (B) are used. That is, in the image sensor, color filters absorbrespective color components from incidence light such that only redlight, green light, and blue light are extracted from the incidencelight. The extracted red, green, and blue light components are caused tobe incident on a solid image pickup element to measure the respectivelight components. As a result, a color image is obtained.

However, many solid image pickup elements have sensitivity to infraredlight in addition to red light, green light, and blue light (visiblelight). In addition, a general color filter does not absorb infraredlight.

Therefore, in an image sensor including color filters of three primarycolors, infrared light is also incident on a solid image pickup elementand measured as a light component of each color.

This infrared light component becomes noise to appropriate red light,green light, and blue light, which causes image quality deterioration ofan image obtained by the image sensor.

Therefore, in the image sensor, an infrared filter that blocks (cuts)infrared light is provided to remove noise generated by infrared light.

In general, an infrared filter has a configuration in which a layerformed of a material that absorbs infrared light or a multi-layer filmthat reflects infrared light using interference is provided on a surface(main surface) of a substrate such as glass or a film.

This infrared filter is typically provided between an optical system forimaging and an image sensor.

However, recently, a reduction in the thickness of an imaging devicethat is provided in a digital camera, a smartphone, or the like isrequired. However, the infrared filter that is provided between theoptical system for imaging and the image sensor is a factor thatinhibits a reduction in the thickness of an imaging device.

On the other hand, WO2014/061188A discloses an image sensor (solid imagepickup element) including: an on-chip lens that is formed of a highrefractive index material; a low refractive index layer that is formedof a low refractive index material and is formed flat on the on-chiplens; and an infrared absorbing layer that is formed of an infraredabsorbing material and is formed above the low refractive index layer,and optionally further including a multi-layer film infrared reflectinglayer that is formed of a multi-layer film including a layer formed of ahigh refractive index material and a layer formed of a low refractiveindex material.

SUMMARY OF THE INVENTION

According to the image sensor described in WO2014/061188A, the infraredfilter is directly formed on the image sensor, and thus the height of animaging device can be reduced.

However, according to an investigation by the present inventors, in thisimage sensor, a multi-layer film infrared reflecting layer that isformed of a multi-layer film including a layer formed of a highrefractive index material and a layer formed of a low refractive indexmaterial is formed by vapor deposition of inorganic materials.Therefore, a coarse particulate defect may be formed in the multi-layerfilm infrared reflecting layer.

In a case where the multi-layer film infrared reflecting layer isprovided adjacent to a solid image pickup element, this defect causessignificant deterioration in image quality, and thus it is necessarythat the multi-layer film infrared reflecting layer is provided at agiven distance from a pixel of the solid image pickup elements. As aresult, the thickness of the image sensor increases.

In addition, a device for manufacturing the solid image pickup elementhas a configuration different from that of device for manufacturing themulti-layer film. Therefore, in order to directly prepare themulti-layer film infrared reflecting layer on the solid image pickupelement, significant improvement of facilities or a complex step such asa step of separately manufacturing the components and transferring themanufactured components is necessary.

Further, it is known that a phenomenon called flaring or ghosting thatoccurs in a case where strong light such as sunlight is incident iscaused by multiple reflection of light between an infrared filter and animage sensor (on-chip lens).

An object of the present invention is to solve the above-describedproblem of the related art and is to provide: a color filter for animage sensor in which an infrared filter can be provided adjacent to asolid image pickup element to block infrared light without forming aparticulate defect or the like and in which the height of an imagingdevice that is provided in a smartphone or the like can be reduced(reduction in thickness); an image sensor including the color filter foran image sensor; and a method of manufacturing the color filter for animage sensor.

In order to solve the problem, according to the present invention, thereis provided a color filter for an image sensor comprising:

-   -   two or more absorbing color filters that absorb light components        having different wavelength ranges; and    -   a cholesteric reflecting layer that is laminated on the        absorbing color filters and in which a right circularly        polarized light cholesteric layer having right circularly        polarized light reflecting properties and a left circularly        polarized light cholesteric layer having left circularly        polarized light reflecting properties are laminated.

In the color filter for an image sensor according to the presentinvention, it is preferable that a gap between the absorbing colorfilters and the cholesteric reflecting layer is 100 μm or less.

In addition, it is preferable that a microlens is provided between theabsorbing color filters and the cholesteric reflecting layer.

In addition, it is preferable that covers the microlens to planarize asurface of the microlens is provided between the microlens and thecholesteric layer.

In addition, it is preferable that the color filter for an image sensorfurther comprises a near infrared absorbing layer having absorptionproperties in a near infrared range.

In addition, it is preferable that an antireflection layer is providedat an interface in contact with air.

In addition, it is preferable that an aligned cholesteric layer isprovided at an interface in contact with the cholesteric reflectinglayer.

In addition, it is preferable that the aligned cholesteric layer is aphoto-aligned film.

In addition, it is preferable that, in a plane of the right circularlypolarized light cholesteric layer and the left circularly polarizedlight cholesteric layer of the cholesteric reflecting layer, a pluralityof reflecting regions that reflect light components having differentwavelength ranges are provided, and reflecting regions that reflectlight components having the same wavelength range are laminated at thesame position in a plane direction.

In addition, it is preferable that the right circularly polarized lightcholesteric layer and the left circularly polarized light cholestericlayer of the cholesteric reflecting layer are formed by curing apolymerizable cholesteric liquid crystal composition.

In addition, it is preferable that the polymerizable cholesteric liquidcrystal composition includes at least one polymerizable liquid crystalhaving a refractive index anisotropy Δn of 0.2 or higher, at least onechiral agent that induces right or left twisting, and a polymerizationinitiator.

In addition, it is preferable that a substrate is provided on a surfaceof the cholesteric reflecting layer opposite to the absorbing colorfilters.

In addition, according to the present invention, there is provided animage sensor comprising:

-   -   the color filter for an image sensor according to the present        invention; and    -   a sensor including solid image pickup elements that are arranged        in a two-dimensional matrix.

In addition, there is provided a first aspect of a method ofmanufacturing a color filter for an image sensor according to thepresent invention, the method comprising:

-   -   a filter forming step of forming two or more absorbing color        filters that absorb light components having different wavelength        ranges on a sensor including solid image pickup elements that        are arranged in a two-dimensional matrix; and    -   a cholesteric reflecting layer forming step of forming a        cholesteric reflecting layer in which a right circularly        polarized light cholesteric layer having right circularly        polarized light reflecting properties and a left circularly        polarized light cholesteric layer having left circularly        polarized light reflecting properties are laminated, the        cholesteric reflecting layer forming step including a step of        forming the right circularly polarized light cholesteric layer        and a step of forming the left circularly polarized light        cholesteric layer.

In the first aspect of the method of manufacturing a color filter for animage sensor according to the present invention, it is preferable that amicrolens forming step of forming a microlens corresponding to a pixelof the solid image pickup elements and a planarizing layer forming stepof forming a planarizing layer that covers the microlens to planarize asurface of the microlens are provided between the filter forming stepand the cholesteric reflecting layer forming step.

In addition, it is preferable that the step of forming the rightcircularly polarized light cholesteric layer in the cholestericreflecting layer forming step includes a step of applying apolymerizable cholesteric liquid crystal composition including a chiralagent that induces right twisting, a step of heating the polymerizablecholesteric liquid crystal composition to form a cholesteric liquidcrystalline phase having right circularly polarized light reflectingproperties, and a step of exposing the cholesteric liquid crystallinephase to ultraviolet light to immobilize the cholesteric liquidcrystalline phase, and it is preferable that the step of forming theleft circularly polarized light cholesteric layer in the cholestericreflecting layer forming step includes a step of applying apolymerizable cholesteric liquid crystal composition including a chiralagent that induces left twisting, a step of heating the polymerizablecholesteric liquid crystal composition to form a cholesteric liquidcrystalline phase having left circularly polarized light reflectingproperties, and a step of exposing the cholesteric liquid crystallinephase to ultraviolet light to immobilize the cholesteric liquidcrystalline phase.

In addition, it is preferable that the first aspect of the method ofmanufacturing a color filter for an image sensor according to thepresent invention further comprises an aligned layer forming step offorming an aligned cholesteric layer on a surface on which thecholesteric reflecting layer is to be formed.

In addition, it is preferable that the aligned cholesteric layer is aphoto-aligned film, and the aligned layer forming step includes a stepof forming a photo-aligned film and a step of irradiating thephoto-aligned film with polarized light to impart an alignmentrestriction force.

In addition, it is preferable that an antireflection layer forming stepof forming an antireflection layer is provided after the cholestericreflecting layer forming step.

In addition, it is preferable that an infrared absorbing layer formingstep of forming a near infrared absorbing layer having absorptionproperties in a near infrared range is provided after the filter formingstep.

Further, it is preferable that, before at least one forming step amongthe respective forming steps, at least one treatment step among abashing treatment step of performing a bashing treatment on a surface onwhich the forming step is to be performed using an organic solvent, aplasma treatment step of performing a plasma treatment on a surface onwhich the forming step is to be performed, and a saponificationtreatment step of performing a saponification treatment on a surface onwhich the forming step is to be performed using an alkaline solution isperformed.

In addition, there is provided a second aspect of a method ofmanufacturing a color filter for an image sensor according to thepresent invention, the method comprising:

-   -   a filter forming step of forming two or more absorbing color        filters that absorb light components having different wavelength        ranges on a sensor including solid image pickup elements that        are arranged in a two-dimensional matrix;    -   a cholesteric reflecting layer forming step of forming a        cholesteric reflecting layer in which a right circularly        polarized light cholesteric layer having right circularly        polarized light reflecting properties and a left circularly        polarized light cholesteric layer having left circularly        polarized light reflecting properties are laminated on one        surface of a substrate; and    -   a bonding step of laminating and bonding the sensor and the        substrate to each other such that the absorbing color filters        and the cholesteric reflecting layer face each other.

In the second aspect of the method of manufacturing a color filter foran image sensor according to the present invention, it is preferablethat, in the bonding step, the solid image pickup element and thesubstrate are bonded to each other such that a distance between thecholesteric reflecting layer and the absorbing color filters is 100 μmor less.

In addition, it is preferable that a microlens forming step of forming amicrolens corresponding to a pixel of the solid image pickup elements isprovided after the filter forming step.

In addition, it is preferable that a bonding layer forming step offorming a bonding layer that covers the microlens to planarize a surfaceof the microlens and bonds the solid image pickup element and thesubstrate to each other is provided after the microlens forming step.

Further, it is preferable that a removing step of removing the substrateis provided after the bonding step.

According to the present invention, an infrared filter having noparticulate defects or the like can be laminated adjacent to an imagepickup element, and the height (thickness) of an imaging device (imagingmodule) that is provided in a digital camera, a smartphone, or the likecan be significantly reduced.

Further, according to the present invention, an infrared filter thatblocks infrared light is provided adjacent to a solid image pickupelement such that the occurrence of flaring and ghosting can besuppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram conceptually showing an example of an image sensoraccording to an embodiment of the present invention including an exampleof a color filter for an image sensor according to an embodiment of thepresent invention.

FIG. 2 is a diagram conceptually showing another example of the imagesensor according to the embodiment of the present invention includinganother example of the color filter for an image sensor according to theembodiment of the present invention.

FIG. 3 is a diagram conceptually showing still another example of theimage sensor according to the embodiment of the present inventionincluding still another example of the color filter for an image sensoraccording to the embodiment of the present invention.

FIG. 4 is a diagram conceptually showing still another example of theimage sensor according to the embodiment of the present inventionincluding still another example of the color filter for an image sensoraccording to the embodiment of the present invention.

FIG. 5 is a diagram conceptually showing still another example of theimage sensor according to the embodiment of the present inventionincluding still another example of the color filter for an image sensoraccording to the embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a color filter for an image sensor, an image sensor, and amethod of manufacturing a color filter for an image sensor according tothe embodiment of the present invention will be described in detailusing a preferable embodiment shown in the accompanying drawings.

In the present invention, numerical ranges represented by “to” includenumerical values before and after “to” as lower limit values and upperlimit values.

Unless specified otherwise, the meaning of “angle” or like includes acase where an error range is generally allowable in the technical field.

In this present invention, “(meth)acrylate” represents “either or bothof acrylate and methacrylate”.

In the present invention, visible light refers to light which can beobserved by human eyes among electromagnetic waves and refers to lightin a wavelength range of 380 to 780 nm Invisible light refers to lightin a wavelength range of shorter than 380 nm or longer than 780 nm.

In addition, although not limited thereto, in visible light, light in awavelength range of 420 to 490 nm refers to blue light (B), light in awavelength range of 495 to 570 nm refers to green light (G), and lightin a wavelength range of 620 to 750 nm refers to red light (R).

Further, in the present invention, infrared light (infrared ray) refersto light in a wavelength range of longer than 780 nm and 1 mm orshorter. In particular, a near infrared light refers to light in awavelength range of longer than 780 nm and 2000 nm or shorter.

FIG. 1 is a diagram conceptually showing an example of an image sensoraccording to an embodiment of the present invention including an exampleof a color filter for an image sensor according to an embodiment of thepresent invention.

An image sensor 10 shown in FIG. 1 includes a sensor main body 12, anabsorbing color filter 14, and a cholesteric reflecting layer 16. Inaddition, in FIG. 1, the color filter for an image sensor according tothe embodiment of the present invention includes the absorbing colorfilter 14 and the cholesteric reflecting layer 16.

In the following description, “color filter for an image sensor”according to the embodiment of the present invention will also simplyreferred to as “color filter”.

The sensor main body 12 includes a solid image pickup element 12 a. Theabsorbing color filter 14 includes a red filter 14R, a green filter 14G,and a blue filter 14B. The cholesteric reflecting layer 16 includes aright circularly polarized light cholesteric layer 16 r and a leftcircularly polarized light cholesteric layer 16 l.

In the example shown in FIG. 1, the sensor main body 12 includes onlythree solid image pickup elements 12 a, and the absorbing color filter14 includes only one red filter 14R, only one green filter 14G, and onlyone blue filter 14B corresponding to the three solid image pickupelements 12 a. However, actually, a plurality of solid image pickupelements 12 a are two-dimensionally arranged. In addition, actually, aplurality of red filters 14R, a plurality of green filters 14G, and aplurality of blue filters 14B are repeatedly formed, for example, in aBayer array.

As described above, the sensor main body 12 includes the solid imagepickup element 12 a.

In general, the sensor main body 12 is a well-known sensor main bodycalled a charge coupled device (CCD) or a complementary metal oxidesemiconductor (CMOS) included in the solid image pickup element 12 asuch as a photodiode.

The solid image pickup element 12 a detects light and functions as alight-receiving element. For detection of light, for example,photoelectric conversion is used. In the sensor main body 12, aplurality of solid image pickup elements 12 a are two-dimensionally aredisposed, and a predetermined number of solid image pickup elements 12 aconstitute one pixel. The solid image pickup element 12 a is formed of,for example, silicon or germanium.

The solid image pickup element 12 a is not particularly limited as longas it can detect light. For example, any one of a PN junction type, ap-intrinsic-n (PIN) junction type, a Schottky type, or an avalanche typecan be used.

In addition to the above-described components, the sensor main body 12includes various well-known members which may be included in awell-known optical sensor called a CCD sensor or a CMOS sensor, forexample, a substrate such as a silicon substrate, a wiring member foroutputting a signal charge obtained from the solid image pickup element12 a to an external device, and a light shielding layer formed of ametal film for preventing light having passed through various colorfilters from being incident on the solid image pickup element 12 aadjacent thereto, or an insulating layer constituting boron phosphorussilicon glass (BPSG).

On a light receiving surface of the sensor main body 12, the absorbingcolor filter 14 is provided.

The absorbing color filter 14 includes the red filter 14R, the greenfilter 14G, and the blue filter 14B, in which any one of the red filter14R, the green filter 14G or the blue filter 14B is providedcorresponding to one solid image pickup element 12 a of the sensor mainbody 12.

The absorbing color filter 14 is a well-known three primary colorabsorbing color filter used in a CCD sensor or the like.

That is, the red filter 14R allows transmission of red light and absorbsvisible light other than red light. The green filter 14G allowstransmission of green light and absorbs visible light other than greenlight. The blue filter 14B allows transmission of blue light and absorbsvisible light other than blue light.

As the absorbing color filter 14, a color filter of a color other thanred, green, and blue may be used. For example, as the absorbing colorfilter 14, a complementary color filter having transmitted light spectrain cyan, magenta, and yellow regions, or a visible cut filter that cutsvisible light and allows transmission of near infrared light can also beused.

Further, as the absorbing color filter 14, two or more selected fromred, green, and blue color filters, a complementary color filter, and avisible cut filter may be used in combination.

On the absorbing color filter 14, that is, on a surface of the absorbingcolor filter 14 opposite to the sensor main body 12, the cholestericreflecting layer 16 is provided. In the following description, “upperside” refers to the upper side in the drawing. That is, the sensor mainbody 12 side refers to “lower side”.

As described above, the cholesteric reflecting layer 16 includes theright circularly polarized light cholesteric layer 16 r and the leftcircularly polarized light cholesteric layer 16 l. Both the rightcircularly polarized light cholesteric layer 16 r and the leftcircularly polarized light cholesteric layer 16 l are obtained byimmobilizing a cholesteric liquid crystalline phase and have wavelengthselective reflecting properties.

As described above, both the right circularly polarized lightcholesteric layer 16 r and the left circularly polarized lightcholesteric layer 16 l are layers obtained by immobilizing a cholestericliquid crystalline phase. The cholesteric liquid crystalline phase haswavelength selective reflecting properties in which selective reflectingproperties are exhibited at a specific wavelength.

A center wavelength λ of the selective reflection of the cholestericliquid crystalline phase depends on a pitch P (=helical cycle) of ahelical structure in the cholesteric liquid crystalline phase andcomplies with an average refractive index n of the cholesteric liquidcrystalline phase and a relationship of λ=n×P. Therefore, the selectivereflection wavelength can be adjusted by adjusting the pitch of thehelical structure. The pitch of the cholesteric liquid crystalline phasedepends on the kind of a chiral agent which is used in combination of apolymerizable liquid crystal compound, or the concentration of thechiral agent added. Therefore, a desired pitch can be obtained byadjusting the kind and concentration of the chiral agent.

In addition, a full width at half maximum Δλ (nm) of a selectivereflection range (circularly polarized light reflection range) whereselective reflection is exhibited depends on a refractive indexanisotropy Δn of the cholesteric liquid crystalline phase and thehelical pitch P and complies with a relationship of Δλ=Δn×P. Therefore,the width of the selective reflection range can be controlled byadjusting the refractive index anisotropy Δn of the cholesteric liquidcrystalline phase. The refractive index anisotropy Δn can be adjusted byadjusting the kinds of liquid crystal compounds for forming the rightcircularly polarized light cholesteric layer 16 r and the leftcircularly polarized light cholesteric layer 16 l and a mixing ratiothereof, and a temperature during alignment immobilization.

As a method of measuring a helical sense and a helical pitch, a methoddescribed in “Introduction to Experimental Liquid Crystal Chemistry”,(the Japanese Liquid Crystal Society, 2007, Sigma Publishing Co., Ltd.),p. 46, and “Liquid Crystal Handbook” (the Editing Committee of LiquidCrystal Handbook, Maruzen Publishing Co., Ltd.), p. 196 can be used.

Reflected light of the cholesteric liquid crystalline phase iscircularly polarized light. Whether or not the reflected circularlypolarized light is right circularly polarized light or left circularlypolarized light is determined depending on a helical twisting directionof the cholesteric liquid crystalline phase. Regarding the selectivereflection of the circularly polarized light by the cholesteric liquidcrystalline phase, in a case where the helical twisting direction of thecholesteric liquid crystalline phase is right, right circularlypolarized light is reflected, and in a case where the helical twistingdirection of the cholesteric liquid crystalline phase is left, leftcircularly polarized light is reflected.

Accordingly, in the cholesteric reflecting layer 16, the rightcircularly polarized light cholesteric layer 16 r is a layer obtained byimmobilizing a right-twisted cholesteric liquid crystalline phase, andthe left circularly polarized light cholesteric layer 16 l is a layerobtained by immobilizing a left-twisted cholesteric liquid crystallinephase.

A direction of rotation of the cholesteric liquid crystalline phase canbe adjusted by adjusting the kinds of liquid crystal compounds forforming the right circularly polarized light cholesteric layer 16 r andthe left circularly polarized light cholesteric layer 16 l and/or thekind of a chiral agent to be added.

The right circularly polarized light cholesteric layer 16 r and/or theleft circularly polarized light cholesteric layer 16 l may have asingle-layer structure or a multi-layer structure.

A wavelength range of light to be reflected, that is, a wavelength rangeof light to be blocked can be widened by sequentially laminating layersin which the center wavelength λ of selective reflection is shifted. Inaddition, as a method of changing a helical pitch in a layer stepwisethat is called a pitch gradient method, a technique of widening awavelength range is also known, and specific examples thereof includemethods described in Nature 378, 467-469 (1995), JP1994-281814A(JP-H6-281814A), and JP4990426B.

Reflection wavelength ranges of the right circularly polarized lightcholesteric layer 16 r and the left circularly polarized lightcholesteric layer 16 l according to the embodiment of the presentinvention can be set to be in any one of a visible range (about 380 to780 nm) or a near infrared range (about 780 to 2000 nm), and a settingmethod thereof is as described above.

In a case where a cholesteric layer is used as an infrared filter, it isnecessary to cover a range up to 1200 nm that is a sensitivity range ofa general silicon photodiode. The lower limit of the wavelength isdetermined based on a relationship with a blocking wavelength range ofthe absorbing color filter and is generally about 700 to 800 nm.

As in the case of the multi-layer film infrared reflecting layer formedof inorganic materials, a reflection type filter formed of a cholestericlayer has angle dependence of the reflection wavelength, and as theincidence angle of incidence light becomes shallow, the wavelength ofreflection wavelength decreases. That is, as the lower limit value ofthe reflection wavelength is set to be lower, coloring (redness) withrespect to oblique light becomes significant, and thus it is necessaryto make an optical design in consideration of the effect of thecoloring. In order to avoid the problem of the coloring with respect tooblique light, it is effective to use the cholesteric reflecting layer16 in combination with an infrared absorbing layer 34 described below,and it is desirable to make design in which the infrared absorbing layer34 having no angle dependence is set on a short wavelength side and thecholesteric reflecting layer covers a long wavelength side. In addition,the cholesteric reflecting layer 16 is also applicable to a selectivewavelength filter that allows or blocks transmission of only nearinfrared light at a specific wavelength.

For example, the image sensor 10 may be prepared using a methodincluding: forming the absorbing color filter 14 including the redfilter 14R, the green filter 14G, and the blue filter 14B on a lightincident surface of the sensor main body 12 (filter forming step); andforming the cholesteric reflecting layer 16 by forming the rightcircularly polarized light cholesteric layer 16 r on the absorbing colorfilter 14 and forming the left circularly polarized light cholestericlayer 16 l on the right circularly polarized light cholesteric layer 16r (cholesteric reflecting layer forming step).

The order of formation of the right circularly polarized lightcholesteric layer 16 r and the left circularly polarized lightcholesteric layer 16 l may be reversed. That is, the image sensor 10 mayhave a configuration in which the left circularly polarized lightcholesteric layer 16 l is provided on the absorbing color filter 14 sideas the lower layer and the right circularly polarized light cholestericlayer 16 r is provided on the left circularly polarized lightcholesteric layer 16 l. Regarding this point, the same shall be appliedto other image sensors.

Further, instead of directly forming the cholesteric reflecting layer 16on the surface of the absorbing color filter 14 (surface on which thecholesteric reflecting layer 16 is to be formed), a configuration offorming the right circularly polarized light cholesteric layer 16 rand/or the left circularly polarized light cholesteric layer 16 l on asubstrate such as a glass substrate and laminating this substrate on theabsorbing color filter 14 may be adopted. In this case, the cholestericreflecting layer 16 may be formed by forming the right circularlypolarized light cholesteric layer 16 r and the left circularly polarizedlight cholesteric layer 16 l on one substrate, or the cholestericreflecting layer 16 may be formed by forming the right circularlypolarized light cholesteric layer 16 r on one substrate, forming theleft circularly polarized light cholesteric layer 16 l on anothersubstrate, and laminating these substrates.

The configuration using the substrate may be used even in a case where aplurality of right circularly polarized light cholesteric layers 16 rand/or a plurality of left circularly polarized light cholesteric layers16 l. In a case where a cholesteric layer having a multi-layerconfiguration is formed using a substrate, the right circularlypolarized light cholesteric layers 16 r and/or the left circularlypolarized light cholesteric layers 16 l may be formed by forming aplurality of cholesteric layers on one substrate. The right circularlypolarized light cholesteric layer 16 r and/or the left circularlypolarized light cholesteric layer 16 l may be formed by laminating onecholesteric layer or a plurality of cholesteric layers on one substrateand laminating a plurality of the substrates.

This configuration using the substrate may be used to form a layer otherthan the cholesteric reflecting layer 16.

As the substrate, for example, various substrates described below asexamples of a substrate 42 may be used.

In addition, it is preferable that, before at least one formation(forming step) among the formation of the absorbing color filter 14(filter forming step) and the formation of the cholesteric reflectinglayer 16, that is, the formation of the right circularly polarized lightcholesteric layer 16 r and the formation of the left circularlypolarized light cholesteric layer 16 l (cholesteric reflecting layerforming step), at least one treatment (treatment step) among a bashingtreatment (bashing treatment step) using an organic solvent, a plasmatreatment (plasma treatment step), and a saponification treatment usingan alkaline solution (saponification treatment step) is performed on asurface on which the cholesteric layer or the like is to be formed(surface on which the forming step is to be performed).

In addition to the formation of the absorbing color filter 14 and/or theformation of the cholesteric reflecting layer 16, it is preferable that,before at least one formation among the formation of a microlens 24(microlens forming step), the formation of a planarizing layer 26(planarizing layer forming step), the formation of an alignedcholesteric layer 32 (aligned layer forming step), the formation of theinfrared absorbing layer 34 (infrared absorbing layer forming step), andthe formation of an antireflection layer 36 (antireflection layerforming step) described below, at least one treatment among the bashingtreatment using an organic solvent, the plasma treatment, and thesaponification treatment using an alkaline solution is performed on asurface on which the cholesteric layer or the like is to be formed.

Further, one or more treatment among the bashing treatment, the plasmatreatment, and the saponification treatment may be optionally performedon a surface of the substrate 42 described below.

In a case where any layer is formed using a coating method, and in acase where a coating solution (coating composition) for forming thelayer includes a fluorine-based cissing inhibitor and/or an interfacealignment agent, the fluorine material may be unevenly distributed on asurface the formed layer. In a case where a coating solution is appliedto the formed surface (coated surface) to further form another layer onthe surface of the layer using a coating method, cissing is likely tooccur in the coating solution, and an appropriate layer may not beformed.

In order to prevent this problem, in general, it is necessary that asurface energy of the coating solution is higher than a surface energyof the surface where the layer is formed, that is, the coated surface.

On the other hand, by performing the bashing treatment on the surfacewhere the layer is to be formed before the formation of the layer, thefluorine material may be removed from the surface where the layer is tobe formed such that the surface energy increases. As a result, thecoating solution is appropriately applied to the surface where the layeris to be formed such that an appropriate layer can be formed.

Any treatment among the bashing treatment using an organic solvent, theplasma treatment, and the saponification treatment may be performedusing a well-known method according to the surface where the layer is tobe formed and/or a material or the like of the material.

The formation of the absorbing color filter 14 may be performed using awell-known method that is performed using a CCD sensor or a CMOS sensor.

On the other hand, the formation of the right circularly polarized lightcholesteric layer 16 r and the left circularly polarized lightcholesteric layer 16 l may be performed, for example, using thefollowing method.

In the following description, in a case where it is not necessary todistinguish the right circularly polarized light cholesteric layer 16 rand the left circularly polarized light cholesteric layer 16 l from eachother, the right circularly polarized light cholesteric layer 16 r andthe left circularly polarized light cholesteric layer 16 l will also becollectively referred to as “cholesteric liquid crystal layer”.

The cholesteric liquid crystal layer can be obtained by immobilizing acholesteric liquid crystalline phase.

The structure in which a cholesteric liquid crystalline phase isimmobilized may be a structure in which the alignment of the liquidcrystal compound as a cholesteric liquid crystalline phase isimmobilized. Typically, the structure in which a cholesteric liquidcrystalline phase is immobilized may be a structure which is obtained bymaking the polymerizable liquid crystal compound to be in a state wherea cholesteric liquid crystalline phase is aligned, polymerizing andcuring the polymerizable liquid crystal compound with ultravioletirradiation, heating, or the like to form a layer having no fluidity,and concurrently changing the state of the polymerizable liquid crystalcompound into a state where the aligned state is not changed by anexternal field or an external force.

The structure in which a cholesteric liquid crystalline phase isimmobilized is not particularly limited as long as the opticalcharacteristics of the cholesteric liquid crystalline phase aremaintained, and the liquid crystal compound does not necessarily exhibitliquid crystallinity. For example, the molecular weight of thepolymerizable liquid crystal compound may be increased by a curingreaction such that the liquid crystallinity thereof is lost.

Examples of a material used for forming the cholesteric liquid crystallayer obtained by immobilizing a cholesteric liquid crystalline phaseinclude a liquid crystal composition including a liquid crystalcompound. It is preferable that the liquid crystal compound is apolymerizable liquid crystal compound.

It is preferable that the liquid crystal composition including a liquidcrystal compound for forming the cholesteric liquid crystal layerfurther includes a surfactant. In addition, the liquid crystalcomposition used for forming the cholesteric liquid crystal layer mayfurther include a chiral agent and a polymerization initiator.

In particular, it is preferable that the liquid crystal composition forforming the right circularly polarized light cholesteric layer 16 r is apolymerizable cholesteric liquid crystal composition including apolymerizable liquid crystal compound and a chiral agent that inducesright twisting and optionally further including a polymerizationinitiator. In addition, it is preferable that the liquid crystalcomposition for forming the left circularly polarized light cholestericlayer 16 l is a polymerizable cholesteric liquid crystal compositionincluding a polymerizable liquid crystal compound and a chiral agentthat induces left twisting and optionally further including apolymerization initiator.

It is preferable that the polymerizable cholesteric liquid crystalcomposition includes one or more polymerizable liquid crystal compoundshaving a refractive index anisotropy Δn of 0.2 or higher.

—Polymerizable Liquid Crystal Compound—

The polymerizable liquid crystal compound may be a rod-shaped liquidcrystal compound or a disk-shaped liquid crystal compound and ispreferably a rod-shaped liquid crystal compound.

Examples of the rod-shaped polymerizable liquid crystal compound forforming the cholesteric liquid crystalline phase include a rod-shapednematic liquid crystal compound. As the rod-shaped nematic liquidcrystal compound, an azomethine compound, an azoxy compound, acyanophenyl compound, a cyanophenyl ester compound, a benzoate compound,a phenyl cyclohexanecarboxylate compound, a cyanophenylcyclohexanecompound, a cyano-substituted phenylpyrimidine compound, analkoxy-substituted phenylpyrimidine compound, a phenyldioxane compound,a tolan compound, or an alkenylcyclohexylbenzonitrile compound ispreferably used. Not only a low-molecular-weight liquid crystal compoundbut also a high-molecular-weight liquid crystal compound can be used.

The polymerizable liquid crystal compound can be obtained by introducinga polymerizable group into the liquid crystal compound. Examples of thepolymerizable group include an unsaturated polymerizable group, an epoxygroup, and an aziridinyl group. Among these, an unsaturatedpolymerizable group is preferable, and an ethylenically unsaturatedpolymerizable group is more preferable. The polymerizable group can beintroduced into the molecules of the liquid crystal compound usingvarious methods. The number of polymerizable groups in the polymerizableliquid crystal compound is preferably 1 to 6 and more preferably 1 to 3.Examples of the polymerizable liquid crystal compound include compoundsdescribed in Makromol. Chem. (1989), Vol. 190, p. 2255, AdvancedMaterials (1993), Vol. 5, p. 107, U.S. Pat. Nos. 4,683,327A, 5,622,648A,US5,770,107A, WO95/022586A, WO95/024455A, WO97/000600A, WO98/023580A,WO98/052905A, JP1989-272551A (JP-H1-272551A), JP1994-016616A(JP-H6-016616A), JP1995-110469A (JP-H7-110469A), JP1999-080081A(JP-H11-080081A), and JP2001-328973A. Two or more polymerizable liquidcrystal compounds may be used in combination. In a case where two ormore polymerizable liquid crystal compounds are used in combination, thealignment temperature can be decreased.

Specific examples of the polymerizable liquid crystal compound includecompounds represented by the following Formulae (1) to (14).

[In Compound (11), X¹ represents 2 to 5 (integer).]

In addition, as described above, in order to obtain a wide bandwidth Δλ(the full width at half maximum Δλ of the selective reflection rangewhere selective reflection is exhibited) and a high reflectivity, it ispreferable that the refractive index anisotropy Δn of the cholestericliquid crystalline phase is high. Accordingly, in order to obtain a widebandwidth and a high reflectivity, it is preferable that a polymerizableliquid crystal compound having a high refractive index anisotropy Δn isused. Specifically, the refractive index anisotropy Δn at 30° C. of thepolymerizable liquid crystal compound used in the liquid crystalcomposition is preferably 0.2 or higher as described above, morepreferably 0.25 or higher, still more preferably 0.3 or higher, and evenstill more preferably 0.35 or higher. The upper limit of the refractiveindex anisotropy Δn of the polymerizable liquid crystal compound is notparticularly limited and is likely to be 0.6 or lower.

As a method of measuring the refractive index anisotropy Δn, A method ofusing a wedge-shaped liquid crystal cell described in, for example,“Liquid Crystal Handbook” (the Editing Committee of Liquid CrystalHandbook, Maruzen Publishing Co., Ltd.), page 202 is generally used. Inthe case of a compound that is likely to be crystallized, the refractiveindex anisotropy Δn can be estimated from an extrapolation value in theevaluation of a mixture of the compound and another liquid crystals.

Examples of the polymerizable liquid crystal compound having a highrefractive index anisotropy Δn include compounds described in U.S. Pat.No. 6,514,578B, JP3999400B, JP4117832B, JP4517416B, JP4836335B,JP5411770B, JP5411771B, JP5510321B, JP5705465B, JP5721484B, andJP5723641B.

Other preferable examples of the polymerizable liquid crystal compoundinclude a polymerizable liquid crystal compound represented by thefollowing Formula (1).

P¹-Sp¹-Y¹A¹-X¹_(n) ₁ A³

A⁴X²-A²_(n) ₂ Y²-Sp²-P²   Formula (1)

In Formula (1), A¹ to A⁴ each independently represent an aromaticcarbocyclic ring or a heterocycle which may have a substituent. Examplesof the aromatic carbocyclic ring include a benzene ring and anaphthalene ring. Examples of the heterocycle include a furan ring, athiophene ring, a pyrrole ring, a pyrroline ring, a pyrrolidine ring, anoxazole ring, an isoxazole ring, a thiazole ring, an isothiazole ring,an imidazole ring, an imidazoline ring, an imidazolidine ring, apyrazole ring, a pyrazoline ring, a pyrazolidine ring, a triazole ring,a furazan ring, a tetrazole ring, a pyran ring, a thiin ring, a pyridinering, a piperidine ring, an oxazine ring, a morpholine ring, a thiazinering, a pyridazine ring, a pyrimidine ring, a pyrazine ring, apiperazine ring, and a triazine ring. In particular, A¹ to A⁴ eachindependently represent preferably an aromatic carbocyclic ring and morepreferably a benzene ring.

The kind of the substituent which may be substituted with the aromaticcarbocyclic ring or the heterocycle is not particularly limited, andexamples thereof include a halogen atom, a cyano group, a nitro group,an alkyl group, a halogen-substituted alkyl group, an alkoxy group, analkylthio group, an acyloxy group, an alkoxycarbonyl group, a carbamoylgroup, an alkyl-substituted carbamoyl group, and an acylamino grouphaving 2 to 6 carbon atoms.

X¹ and X² each independently represent a single bond, —COO—, —OCO—,—CONH—, —NHCO—, —CH₂CH₂—, —OCH₂—, —CH₂O—, —CH═CH—, —CH═CH—COO—,—OCO—CH═CH—, or —C≡C—. Among these, a single bond, —COO—, —CONH—,—NHCO—, or —C≡C— is preferable.

Y¹ and Y² each independently represent a single bond, —O—, —S—, —CO—,—COO—, —OCO—, —CONH—, —NHCO—, —CH═CH—, —CH═CH—COO—, —OCO—CH═CH—, or—C≡C—. Among these, —O— is preferable.

Sp¹ and Sp² each independently represent a single bond or a carbon chainhaving 1 to 25 carbon atoms. The carbon chain may be linear, branched,or cyclic. As the carbon chain, a so-called alkyl group is preferable.Among these, an alkyl group having 1 to 10 carbon atoms is morepreferable.

P¹ and P² each independently represent a hydrogen atom or apolymerizable group, and at least one of P¹ or P² represents apolymerizable group. Examples of the polymerizable group include theexamples of the polymerizable group which is included in the liquidcrystal compound having a polymerizable group.

n¹ and n² each independently represent an integer of 0 to 2. In a casewhere n¹ or n² represents 2, a plurality of A¹′s, A²′s, X¹′s, or X²′smay be the same as or different from each other.

Specific examples of the polymerizable liquid crystal compoundrepresented by Formula (1) include compounds represented by thefollowing Formulae (1-1) to (1-30).

In addition, as a polymerizable liquid crystal compound other than theabove-described examples, for example, a cyclic organopolysiloxanecompound having a cholesteric phase described in JP1982-165480A(JP-S57-165480A) can be used. Further, as the above-describedhigh-molecular-weight liquid crystal compound, for example, a polymer inwhich a liquid crystal mesogenic group is introduced into a main chain,a side chain, or both a main chain and a side chain, a polymercholesteric liquid crystal in which a cholesteryl group is introducedinto a side chain, a liquid crystal polymer described in JP1997-133810A(JP-H9-133810A), and a liquid crystal polymer described inJP1999-293252A (JP-H11-293252A) can be used.

In addition, the addition amount of the polymerizable liquid crystalcompound in the liquid crystal composition is preferably 75 to 99.9 mass%, more preferably 80 to 99 mass %, and still more preferably 85 to 90mass % with respect to the solid content mass (mass excluding a solvent)of the liquid crystal composition.

—Chiral Agent (Optically Active Compound)—The chiral agent has afunction of causing a helical structure of a cholesteric liquidcrystalline phase to be formed. The chiral agent may be selecteddepending on the purpose because a helical twisting direction or ahelical pitch derived from the compound varies.

That is, in a case where the right circularly polarized lightcholesteric layer 16 r is formed, a chiral agent that induces righttwisting may be used. In a case where the left circularly polarizedlight cholesteric layer 16 l is formed, a chiral agent that induces lefttwisting may be used.

The chiral agent is not particularly limited, and a well-known compound(for example, Liquid Crystal Device Handbook (No. 142 Committee of JapanSociety for the Promotion of Science, 1989), Chapter 3, Article 4-3,chiral agent for twisted nematic (TN) or super twisted nematic (STN), p.199), isosorbide, or an isomannide derivative can be used.

In general, the chiral agent includes an asymmetric carbon atom.However, an axially asymmetric compound or a surface asymmetric compoundnot having an asymmetric carbon atom can also be used as a chiral agent.Examples of the axially asymmetric compound or the surface asymmetriccompound include binaphthyl, helicene, paracyclophane, and derivativesthereof. The chiral agent may include a polymerizable group. In a casewhere both the chiral agent and the liquid crystal compound have apolymerizable group, a polymer which includes a repeating unit derivedfrom the polymerizable liquid crystal compound and a repeating unitderived from the chiral agent can be formed due to a polymerizationreaction of a polymerizable chiral agent and the polymerizable liquidcrystal compound. In this aspect, it is preferable that thepolymerizable group included in the polymerizable chiral agent is thesame as the polymerizable group included in the polymerizable liquidcrystal compound. Accordingly, the polymerizable group of the chiralagent is preferably an unsaturated polymerizable group, an epoxy group,or an aziridinyl group, more preferably an unsaturated polymerizablegroup, and still more preferably an ethylenically unsaturatedpolymerizable group.

In addition, the chiral agent may be a liquid crystal compound.

In a case where the chiral agent includes a photoisomerization group, apattern having a desired reflection wavelength corresponding to anemission wavelength can be formed by photomask exposure of an actinicray or the like after coating and alignment, which is preferable. As thephotoisomerization group, an isomerization portion of a photochromiccompound, an azo group, an azoxy group, or a cinnamoyl group ispreferable. As a specific compound, compounds described inJP2000-147236A, JP2002-080478A, JP2002-080851A, JP2002-179633A,JP2002-179668A, JP2002-179669A, JP2002-179670A, JP2002-179681A,JP2002-179682A, JP2002-302487A, JP2002-338575A, JP2002-338668A,JP2003-306490A, JP2003-306491A, JP2003-313187A, JP2003-313188A,JP2003-313189A, and JP2003-313292A can be used.

The content of the chiral agent in the liquid crystal composition ispreferably 0.01 to 200 mol % and more preferably 1 to 30 mol % withrespect to the amount of the polymerizable liquid crystal compound.

—Polymerization Initiator—

In a case where the liquid crystal composition includes a polymerizablecompound, it is preferable that the liquid crystal composition includesa polymerization initiator. In an aspect where a polymerization reactionprogresses with ultraviolet irradiation, it is preferable that thepolymerization initiator is a photopolymerization initiator whichinitiates a polymerization reaction with ultraviolet irradiation.Examples of the photopolymerization initiator include an α-carbonylcompound (described in U.S. Pat. Nos. 2,367,661A and 2,367,670A), anacyloin ether (described in U.S. Pat. No. 2,448,828A), anα-hydrocarbon-substituted aromatic acyloin compound (described in U.S.Pat. No. 2,722,512A), a polynuclear quinone compound (described in U.S.Pat. Nos. 3,046,127A and 2,951,758A), a combination of a triarylimidazole dimer and p-aminophenyl ketone (described in U.S. Pat. No.3,549,367A), an acridine compound and a phenazine compound (described inJP1985-105667A (JP-S60-105667A) and U.S. Pat. No. 4,239,850A), and anoxadiazole compound (described in U.S. Pat. No. 4,212,970A).

The content of the photopolymerization initiator in the liquid crystalcomposition is preferably 0.1 to 20 mass % and more preferably 0.5 to 12mass % with respect to the content of the polymerizable liquid crystalcompound.

—Crosslinking Agent—

In order to improve the film hardness after curing and to improvedurability, the liquid crystal composition may include a crosslinkingagent. As the crosslinking agent, a curing agent which can performcuring with ultraviolet light, heat, moisture, or the like can bepreferably used.

The crosslinking agent is not particularly limited and can beappropriately selected depending on the purpose. Examples of thecrosslinking agent include: a polyfunctional acrylate compound such astrimethylol propane tri(meth)acrylate or pentaerythritoltri(meth)acrylate; an epoxy compound such as glycidyl (meth)acrylate orethylene glycol diglycidyl ether; an aziridine compound such as 2,2-bishydroxymethyl butanol-tris[3-(1-aziridinyl)propionate] or4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; an isocyanatecompound such as hexamethylene diisocyanate or a biuret type isocyanate;a polyoxazoline compound having an oxazoline group at a side chainthereof; and an alkoxysilane compound such as vinyl trimethoxysilane orN-(2-aminoethyl)-3-aminopropyltrimethoxysilane. In addition, dependingon the reactivity of the crosslinking agent, a well-known catalyst canbe used, and not only film hardness and durability but also productivitycan be improved. Among these crosslinking agents, one kind may be usedalone, or two or more kinds may be used in combination.

The content of the crosslinking agent is preferably 3 to 20 mass % andmore preferably 5 to 15 mass % with respect to the solid content mass ofthe liquid crystal composition. In a case where the content of thecrosslinking agent is in the above-described range, an effect ofimproving a crosslinking density can be easily obtained, and thestability of a cholesteric liquid crystalline phase is further improved.

—Polymerization Inhibitor—

In order to improve storage, the liquid crystal composition may includea polymerization inhibitor.

Examples of the polymerization inhibitor include hydroquinone,hydroquinone monomethyl ether, phenothiazine, benzoquinone, hinderedamine (HALS), and derivatives thereof. Among these polymerizationinhibitors, one kind may be used alone, or two or more kinds may be usedin combination.

The content of the polymerization inhibitor is preferably 0 to 10 mass %and more preferably 0 to 5 mass % with respect to the solid content massof the liquid crystal composition.

In a case where the cholesteric liquid crystal layer is formed, it ispreferable that the liquid crystal composition is used as liquid.

The liquid crystal composition may include a solvent. The solvent is notparticularly limited and can be appropriately selected depending on thepurpose. An organic solvent is preferably used.

The organic solvent is not particularly limited and can be appropriatelyselected depending on the purpose. Examples of the organic solventinclude a ketone such as methyl ethyl ketone, methyl isobutyl ketone,cyclohexanone, or cyclopentanone, an alkyl halide, an amide, asulfoxide, a heterocyclic compound, a hydrocarbon, an ester, and anether. Among these solvents, one kind may be used alone, or two or morekinds may be used in combination. Among these, a ketone is preferable inconsideration of an environmental burden. The above-described componentsuch as the above-described monofunctional polymerizable monomer mayfunction as the solvent.

The right circularly polarized light cholesteric layer 16 r may beformed using, for example, a method including: a step of applying aliquid crystal composition for forming the right circularly polarizedlight cholesteric layer 16 r including a chiral agent that induces righttwisting to the absorbing color filter 14; a step of heating the liquidcrystal composition to form a cholesteric liquid crystalline phasehaving right circularly polarized light reflecting properties; and astep of irradiating (exposing) the cholesteric liquid crystalline phasewith ultraviolet light to immobilize the cholesteric liquid crystallinephase.

On the other hand, the left circularly polarized light cholesteric layer16 l may be formed using, for example, a method including: a step ofapplying a liquid crystal composition for forming the left circularlypolarized light cholesteric layer 16 l including a chiral agent thatinduces left twisting to the right circularly polarized lightcholesteric layer 16 r that is formed first; a step of heating theliquid crystal composition to form a cholesteric liquid crystallinephase having right circularly polarized light reflecting properties; anda step of irradiating (exposing) the cholesteric liquid crystallinephase with ultraviolet light to immobilize the cholesteric liquidcrystalline phase.

The application, drying, and ultraviolet irradiation of the liquidcrystal composition may be performed using a well-known method.

Here, as described above, as the chiral agent, a chiral agent having aportion (photoisomerization group) such as a cinnamoyl group that isisomerized by light can be used. In a case where the chiral agent havinga photoisomerization group is used as the chiral agent of the liquidcrystal composition, the liquid crystal composition may be irradiatedwith weak patterned ultraviolet light once or more to isomerize thephotoisomerization group after being applied and heated, and then may beirradiated with ultraviolet light to immobilize the cholesteric liquidcrystalline phase.

Alternatively, the liquid crystal composition may be irradiated withstrong patterned ultraviolet light for immobilizing the cholestericliquid crystalline phase so as to be partially cured, a non-exposedportion or the entire surface may be irradiated with weak ultravioletlight to isomerize the photoisomerization group, and then the liquidcrystal composition may be irradiated with ultraviolet light forimmobilizing the cholesteric liquid crystalline phase.

As a result, in a plane of the right circularly polarized lightcholesteric layer 16 r and the left circularly polarized lightcholesteric layer 16 l, a plurality of reflecting regions that reflectlight components having different wavelength ranges can be provided. Inthis case, in the right circularly polarized light cholesteric layer 16r and the left circularly polarized light cholesteric layer 16 l, it ispreferable that reflecting regions that reflect light components havingthe same wavelength range are laminated at the same position in a planedirection.

In addition, by adjusting a temperature during ultraviolet irradiation,the reflection wavelength range can also be adjusted. By irradiating thecholesteric liquid crystalline phase with patterned ultraviolet lightwhile adjusting the temperature, in a plane of the right circularlypolarized light cholesteric layer 16 r and the left circularly polarizedlight cholesteric layer 16 l, a plurality of reflecting regions thatreflect light components having different wavelength ranges can beprovided. In particular, by irradiating the cholesteric liquidcrystalline phase with ultraviolet light in a state where the liquidcrystal composition is heated to an isotropic phase temperature orhigher, a transmission region having no reflection properties in anywavelength range can be formed in a plane.

Hereinafter, the action of the image sensor 10 will be described. In thefollowing description, for example, the cholesteric reflecting layer 16reflects (blocks) near infrared light in a wavelength range of longerthan 780 nm and 1200 nm or shorter.

In a case where light is incident on the image sensor 10, first, leftcircularly polarized light of near infrared light in a wavelength rangeof longer than 780 nm and 1200 nm or shorter is reflected from the leftcircularly polarized light cholesteric layer 16 l, and the other lightcomponents transmit through the left circularly polarized lightcholesteric layer 16 l and are reflected from the right circularlypolarized light cholesteric layer 16 r.

In a case where light is incident on the right circularly polarizedlight cholesteric layer 16 r, right circularly polarized light of nearinfrared light in a wavelength range of longer than 780 nm and 1200 nmor shorter is reflected from the right circularly polarized lightcholesteric layer 16 r, and the other light components transmit throughthe right circularly polarized light cholesteric layer 16 r.Accordingly, as a result, all the near infrared light in a wavelengthrange of longer than 780 nm and 1200 nm or shorter is blocked.

Light having transmitted through the right circularly polarized lightcholesteric layer 16 r is converted into red light, green light, or bluelight by any one of the red filter 14R, the green filter 14G, or theblue filter 14B in the absorbing color filter 14, is measured by thesolid image pickup element 12 a, and is output as image data.

As described above, in the image sensor 10 according to the embodimentof the present invention, near infrared light in a wavelength range oflonger than 780 nm and 1200 nm or shorter to which the solid imagepickup element 12 a has sensitivity is removed, and red light, greenlight, and blue light can be measured. Therefore, the amount of noisecaused by infrared light is small, and appropriate image data can beoutput.

In addition, in the related art, an infrared filter that blocks (cuts)infrared light is separately provided distant from an image sensor.However, in the embodiment of the present invention, the infrared filtercan be laminated on or incorporated into the image sensor 10 as thecholesteric reflecting layer 16. Therefore, the height (thickness) of animaging device (imaging module) including the image sensor 10 can besignificantly reduced.

Further, the cholesteric reflecting layer 16 as the infrared filter canbe formed with a coating method using a liquid crystal composition.Therefore, the infrared filter having no particulate defects or the likethat is difficult to be formed by vapor deposition of inorganic layersas in the case of a multi-layer film infrared reflecting layer can beformed, and deterioration of image quality caused by defects can also beprevented.

FIG. 2 conceptually shows another example of the image sensor accordingto the embodiment of the present invention including another example ofthe color filter according to the embodiment of the present invention.

An image sensor 20 shown in FIG. 2 includes the sensor main body 12, theabsorbing color filter 14, the microlens 24, the planarizing layer 26,and the cholesteric reflecting layer 16. The cholesteric reflectinglayer 16 includes the right circularly polarized light cholesteric layer16 r and the left circularly polarized light cholesteric layer 16 l. Inthe example shown in FIG. 2, the color filter according to theembodiment of the present invention includes the absorbing color filter14, the microlens 24, the planarizing layer 26, and the cholestericreflecting layer 16.

The image sensor 20 shown in FIG. 2 has the same configuration as theimage sensor 10 shown in FIG. 1, except that the microlens 24 and theplanarizing layer 26 are provided between the absorbing color filter 14and the cholesteric reflecting layer 16. Therefore, the same members arerepresented by the same reference numerals, and different members willbe mainly described below.

In the image sensor 20 shown in FIG. 2, the microlens 24 is providedcorresponding to each of the red filter 14R, the green filter 14G, andthe blue filter 14B in the absorbing color filter 14, that is,corresponding to each of the solid image pickup elements 12 a.

The microlens 24 is a convex lens in which the center is thicker than anedge, and collects light on the solid image pickup element 12 a. All themicrolenses 28 have the same shape.

The microlens 24 can be formed of various well-known materials as longas it satisfies optical characteristics that are necessary as a lens.For example, the microlens 24 is formed of a resin material, but thepresent invention is not limited thereto. Examples of the resin materialused for the microlens 24 include a styrene resin, a (meth)acrylicresin, a styrene-acrylic copolymer resin, and a siloxane resin.

The planarizing layer 26 planarizes a cholesteric reflecting layer16-side surface on the microlens 24 as a convex lens. The planarizinglayer 26 may also function as a bonding layer (adhesive layer) foradhesion with an upper layer. In the example shown in the drawing, theupper layer above the planarizing layer 26 is the cholesteric reflectinglayer 16, specifically, the right circularly polarized light cholestericlayer 16 r.

The planarizing layer 26 is not particularly limited as long as it hassufficient light-transmitting property, and is formed of, for example,various resin materials. Examples of the resin material for forming theplanarizing layer 26 include a fluorine-containing silane compound suchas a fluorine-containing siloxane resin, a (meth)acrylic resin, astyrene resin, and an epoxy resin.

It is preferable that a refractive index of the microlens 24 is higherthan that of the planarizing layer 26.

In addition, instead of providing the planarizing layer 26, supportmeans for supporting the cholesteric reflecting layer 16 to be distantfrom the microlens 24 may be provided and an air layer may be providedbetween the microlens 24 and the cholesteric reflecting layer 16 suchthat this air layer functions as the planarizing layer 26 thatplanarizes the surface of the microlens 24.

In a case where any layer is provided between the absorbing color filter14 and the cholesteric reflecting layer 16 as in the case of the imagesensor 20 shown in FIG. 2, it is preferable that a gap between theabsorbing color filter 14 and the cholesteric reflecting layer 16 is 100μm or less. As the layer provided between the absorbing color filter 14and the cholesteric reflecting layer 16, for example, the air layer isused.

As a result, the occurrence of ghosting in which light havingtransmitted through the respective color filters of the absorbing colorfilter 14 is incident on the solid image pickup element adjacent to thefilter due to internal reflection or the like instead of being incidenton the solid image pickup element 12 a immediately below the filter canbe suppressed.

The image sensor 20 shown in FIG. 2 can be prepared by providing a stepof forming the microlens 24 on the absorbing color filter 14 (microlensforming step) and a step of forming the planarizing layer 26 that coversthe microlens 24 (planarizing layer forming step) between the formationof the absorbing color filter 14 (filter forming step) and the formationof the cholesteric reflecting layer 16 (cholesteric reflecting layerforming step) in the manufacturing of the image sensor 10.

The microlens 24 may be formed using a well-known method correspondingto a material for forming the microlens 24. In addition, the planarizinglayer 26 may also be formed using a well-known method corresponding to amaterial for forming the planarizing layer 26.

FIG. 3 conceptually shows still another example of the image sensoraccording to the embodiment of the present invention including stillanother example of the color filter according to the embodiment of thepresent invention.

An image sensor 30 shown in FIG. 3 includes the sensor main body 12, theabsorbing color filter 14, the microlens 24, the planarizing layer 26,the aligned cholesteric layer 32, the cholesteric reflecting layer 16(the right circularly polarized light cholesteric layer 16 r and theleft circularly polarized light cholesteric layer 16 l), the infraredabsorbing layer 34, and the antireflection layer 36. In the exampleshown in FIG. 3, the color filter according to the embodiment of thepresent invention includes the absorbing color filter 14, the microlens24, the planarizing layer 26, the aligned cholesteric layer 32, thecholesteric reflecting layer 16, the infrared absorbing layer 34, andthe antireflection layer 36.

The image sensor 30 shown in FIG. 3 has the same configuration as theimage sensor 20 shown in FIG. 2, except that the aligned cholestericlayer 32, the infrared absorbing layer 34, and the antireflection layer36 are provided. Therefore, the same members are represented by the samereference numerals, and different members will be mainly describedbelow.

The aligned cholesteric layer 32 is a layer for maintaining thealignment of the cholesteric liquid crystalline phase in the rightcircularly polarized light cholesteric layer 16 r and the leftcircularly polarized light cholesteric layer 16 l.

For the aligned cholesteric layer 32, various well-known materials usedas the aligned film of the cholesteric liquid crystal layer can be used.

It is preferable that the aligned cholesteric layer 32 is aphoto-aligned film. For example, the photo-aligned film is irradiatedwith linearly polarized light or oblique non-polarized light at awavelength at which a photochemical reaction occurs in a photochemicalmolecule such as an azobenzene polymer or polyvinyl cinnamate such thatanisotropy is imparted to the surface of the photo-aligned film. As aresult, a molecular major axis of the outermost surface of the film isaligned by incidence light, and an alignment restriction force thataligns liquid crystals in contact with the molecule of the outermostsurface is generated.

Examples of the material of the photo-aligned film include not only theabove-described materials but also any materials that impart anisotropyto a film surface due to any reaction among photoisomerization,photodimerization, photocyclization, photocrosslinking,photodegradation, and photodegradation-bonding by irradiation oflinearly polarized light at a wavelength at which a photochemicalreaction occurs in a photochemical molecule. For example, variousphoto-aligned film materials described in “Masaki Hasegawa, Journal ofthe Liquid Crystal Society of Japan, Vol. 3 No. 1, p. 3 (1999)” or“Yasumasa Takeuchi, Journal of the Liquid Crystal Society of Japan, Vol.3 No. 4, p. 262 (1999)” can be used.

The aligned cholesteric layer 32 may be included in the image sensor 10shown in FIG. 1 that is described above and an image sensor 40 shown inFIG. 4 and an image sensor 50 shown in FIG. 5 that are described below.

The infrared absorbing layer 34 is an absorbing infrared filter thatabsorbs and blocks infrared light in a predetermined wavelength range.

For example, the infrared absorbing layer 34 absorbs and blocks infraredlight in a wavelength range different from infrared light that isblocked by the cholesteric reflecting layer 16. For example, theinfrared absorbing layer 34 as a near infrared absorbing layer absorbsand blocks light in a near infrared range (infrared light on a shortwavelength side) of longer than 780 nm and 820 nm or shorter, and thecholesteric reflecting layer 16 blocks infrared light on a longerwavelength side.

For example, the infrared absorbing layer 34 includes an infraredabsorbing material having an infrared absorbing function. For example,the infrared absorbing layer 34 is formed of a mixture of an infraredabsorbing colorant and a binder resin.

As the infrared absorbing colorant, various well-known materials can beused according to an absorption wavelength range.

Specifically, examples of the infrared absorbing colorant includecolorants having, as a main skeleton, a dithiol complex, an aminothiolcomplex, phthalocyanine, naphthalocyanine, a copper phosphate complex, anitroso compound, or a metal complex thereof. Examples of the metalportion in the complex include iron, magnesium, nickel, cobalt, steel,vanadium, zinc, palladium, platinum, titanium, indium, and tin. Inaddition, examples of an element in the ligand portion include organicligands having a portion such as halogens, an amine group, a nitrogroup, or a thiol group. Further, a substituent such as an alkyl group,a hydroxyl group, a carboxyl group, an amino group, a nitro group, acyano group, a fluorinated alkyl group, or an ether group may beintroduced.

In addition, preferable examples of the infrared absorbing colorantinclude a methine dye such as cyanine or merocyanine and an organiccompound such as triarylmethane, squarylium, anthraquinone,naphthoquinone, quaterrylene, perylene, rutile, immonium, diimmonium,croconium, oxanol, diketo pyrrolo pyrrole, or an aluminum salt. Further,other examples of the infrared absorbing colorant include a metal oxidesuch as indium tin oxide (ITO), aluminum doped zinc oxide (AZO),tungsten oxide, antimony oxide, or cesium tungsten oxide.

The antireflection layer 36 reduces a difference in refractive indexbetween the infrared absorbing layer 34 and air to prevent lightincident on the image sensor 30 from being reflected from an interfacebetween the infrared absorbing layer 34 and air or to prevent lightincident from the lower layer side to the infrared absorbing layer 34from being reflected from an interface between the infrared absorbinglayer 34 and air such that noise generated by the light being incidenton the solid image pickup element 12 a is prevented.

A material for forming the antireflection layer 36 is not particularlylimited and may be an organic material or an inorganic material. Fromthe viewpoint of durability, an inorganic material is preferable.Examples of the inorganic material include an inorganic resin (siloxaneresin) and inorganic particles. Among these, it is preferable that theantireflection layer 36 includes inorganic particles. In addition, asthe antireflection layer 36, various well-known antireflection layersthat can reduce a difference in refractive index between the infraredabsorbing layer 34 and air and are used in an optical element or anoptical device can be used as long as they have sufficient transparency,and examples thereof include a dielectric film formed of any one ofaluminum oxide, magnesium fluoride, zirconium oxide, or silicon oxide,and a dielectric multi-layer film in which a plurality of dielectricfilms are laminated.

The image sensor 30 shown in FIG. 3 can be prepared using a methodincluding: forming the aligned cholesteric layer 32 on the surface ofthe absorbing color filter 14, that is, the surface where thecholesteric reflecting layer 16 is formed after the formation of theabsorbing color filter 14 in the manufacturing of the image sensor 20(aligned layer forming step); forming the cholesteric reflecting layer16; forming the infrared absorbing layer 34 (near infrared absorbinglayer) (infrared absorbing layer forming step); and forming theantireflection layer 36 (antireflection layer forming step).

The formation of the aligned cholesteric layer 32, the infraredabsorbing layer 34, and the antireflection layer 36 may be performedusing a well-known method according to a material for forming the layer.

Here, as described above, it is preferable that the aligned cholestericlayer 32 is a photo-aligned film. In this case, it is preferable thatthe formation of the aligned cholesteric layer 32 (aligned layer formingstep) includes a step of forming a photo-aligned film and a step ofirradiating the formed photo-aligned film with polarized light to impartan alignment restriction force.

Further, the formation of the infrared absorbing layer 34 (infraredabsorbing layer forming step) may be performed before the step offorming the right circularly polarized light cholesteric layer 16 r orbefore the step of forming the left circularly polarized lightcholesteric layer 16 l. That is, the formation of the infrared absorbinglayer 34 may be performed at any timing as long as it is performed afterthe formation of the absorbing color filter 14 (filter forming step) orafter the formation of the planarizing layer 26 (planarizing layerforming step).

In addition, in a case where the infrared absorbing layer 34 is formedbefore the formation of the cholesteric reflecting layer 16 and thealigned cholesteric layer 32 is formed, the formation of the alignedcholesteric layer 32 is performed between the formation of the infraredabsorbing layer 34 and the formation of the right circularly polarizedlight cholesteric layer 16 r or between the formation of the infraredabsorbing layer 34 and the formation of the left circularly polarizedlight cholesteric layer 16 l.

In the image sensor according to the embodiment of the presentinvention, that is, the color filter for an image sensor according tothe embodiment of the present invention, an ultraviolet absorbing layeror an oxygen barrier layer may be further provided as an upper layerabove the cholesteric reflecting layer 16 in FIGS. 1 to 3, that is, onan upper side above the cholesteric reflecting layer 16.

As a result, deterioration of the cholesteric reflecting layer 16 can besuppressed, and stability of the image sensor can also be improved.

The ultraviolet absorbing layer is a layer including an ultravioletabsorber. Accordingly, the ultraviolet absorbing layer may be oneseparate layer not having other functions or may be a layer that isobtained by adding an ultraviolet absorber to a layer having anyfunction to exhibit a function as an ultraviolet absorbing layer.

In a case where the image sensor according to the embodiment of thepresent invention includes the ultraviolet absorbing layer, variousconfigurations may be adopted. It is preferable that the ultravioletabsorbing layer is provided at a position where light is incident firstbefore being incident on the cholesteric reflecting layer 16 or theinfrared absorbing layer 34. That is, in a case where an ultravioletabsorber is added to a layer having any function to exhibit a functionas an ultraviolet absorbing layer, it is preferable that the ultravioletabsorber is added to a layer (in the member) where light is incidentfirst before being incident on the cholesteric reflecting layer 16 orthe infrared absorbing layer 34.

For example, it is preferable that the ultraviolet absorber is added toany layer that is disposed between a glass plate disposed on the outdoorside and the cholesteric reflecting layer 16 and the infrared absorbinglayer 34. Alternatively, it is preferable that the ultraviolet absorbinglayer is provided between a glass plate disposed on the outdoor side andthe cholesteric reflecting layer 16 and the infrared absorbing layer 34.Alternatively, it is also preferable that the ultraviolet absorber isadded to an intermediate film that adheres to a glass plate disposed onthe outdoor side or added to the glass plate itself disposed on theoutdoor side.

The kind of the ultraviolet absorber is not particularly limited and canbe appropriately selected depending on the purpose.

Examples of the ultraviolet absorber include a benzotriazole compound, abenzodithiol compound, a coumarin compound, a benzophenone compound, asalicylic acid ester compound, and a cyanoacrylate compound. Inaddition, for example, titanium oxide and/or zinc oxide can also be usedas the ultraviolet absorber. Other examples of the ultraviolet absorberinclude a commercially available product such as Tinuvin 326, 328, and479 (all of which are manufactured by Chiba Japan).

In addition, as the ultraviolet absorber, for example, an aminodienecompound, a salicylate compound, a benzophenone compound, abenzotriazole compound, an acrylonitrileacrylonitrile compound, or atriazine compound can also be preferably used. Specific examples of theultraviolet absorber include compounds described in JP2013-068814A. Inaddition, as the benzotriazole compound, MYUA series (manufactured byMiyoshi Oil&Fat Co., Ltd.; The Chemical Daily, Feb. 1, 2016) may beused.

In the ultraviolet absorbing layer (layer including the ultravioletabsorber), the addition amount of the ultraviolet absorber is notparticularly limited and may be appropriately set according to thepurpose and the ultraviolet absorber to be used.

Here, in a case where the ultraviolet absorbing layer has an action ofadjusting the transmittance of ultraviolet light having a wavelength of380 nm or shorter to be 0.1% or lower, deterioration of the cholestericreflecting layer 16 can be significantly reduced, and yellowing of theimage sensor (the color filter for an image sensor) can be significantlyreduced. Accordingly, it is preferable that the addition amount of theultraviolet absorber in the ultraviolet absorbing layer is adjusted suchthat the above-described transmittance of ultraviolet light can beachieved.

In addition, as described above, the image sensor according to theembodiment of the present invention may include an oxygen barrier layer.

The oxygen barrier layer is used in order to prevent penetration ofoxygen into a lower layer such that deterioration caused by oxygen isprevented. Accordingly, the oxygen barrier layer is particularlyeffective in a case where a material used for the cholesteric reflectinglayer 16 and/or the infrared absorbing layer 34 may cause oxidationdegradation.

As the oxygen barrier layer, an organic deposited film or an inorganicdeposited film may be used. From the viewpoint of durability, aninorganic deposited film is preferable. In a case where the inorganicdeposited film is used as the antireflection layer 36, theantireflection layer 36 can also function as the oxygen barrier layer.

In addition, it is also preferable that a sheet-like material such asglass having a high oxygen barrier function is laminated on an upperlayer as the oxygen barrier layer. At this time, as shown in the secondaspect of the method of manufacturing a color filter for an image sensordescribed below, it is preferable to use a manufacturing method in whichthe cholesteric reflecting layer 16 that is formed in advance on anothersubstrate (the substrate 42 such as glass) is bonded to the sensorincluding the absorbing color filter.

FIG. 4 conceptually shows still another example of the image sensoraccording to the embodiment of the present invention including stillanother example of the color filter according to the embodiment of thepresent invention.

The image sensor 40 shown in FIG. 4 includes the sensor main body 12,the absorbing color filter 14, the microlens 24, the planarizing layer26, the cholesteric reflecting layer 16, and the substrate 42. In theexample shown in FIG. 4, the color filter according to the embodiment ofthe present invention includes the absorbing color filter 14, themicrolens 24, the planarizing layer 26, the cholesteric reflecting layer16, and the substrate 42.

The image sensor 40 shown in FIG. 4 has the same configuration as theimage sensor 20 shown in FIG. 2, except that the substrate 42 isprovided. Therefore, the same members are represented by the samereference numerals, and different members will be mainly describedbelow.

In addition, the configuration in which the substrate 42 is provided isapplicable to the image sensor 10 shown in FIG. 1.

The substrate 42 is, for example, a sheet-like material formed of aresin material.

Examples of a material for forming the substrate 42 include glass,triacetyl cellulose (TAC), polyethylene terephthalate (PET),polycarbonate, polyvinyl chloride, acryl, polyolefin, andpolycycloolefin.

The image sensor 40 including the substrate 42 may be prepared, forexample, as follows.

First, as described above, the absorbing color filter 14 is formed onthe sensor main body 12 (filter forming step), the microlens 24 isformed on the absorbing color filter 14 (microlens forming step), andthe planarizing layer 26 that planarizes the surface of the microlens 24is formed on the microlens 24.

At this time, it is preferable that the planarizing layer 26 is formedusing a pressure sensitive adhesive or an adhesive such that theplanarizing layer 26 functions as a bonding layer for adhesion with thesubstrate 42 described below. In this case, the formation of theplanarizing layer 26 corresponds to the bonding layer forming step inthe embodiment of the present invention.

In a case where the substrate 42 is used in the image sensor 10 shown inFIG. 1, the formation of the microlens 24 and the formation of theplanarizing layer 26 are not performed.

On the other hand, the cholesteric reflecting layer 16 is formed on thesurface of the substrate 42 by performing the step of forming the leftcircularly polarized light cholesteric layer 16 l and the step offorming the right circularly polarized light cholesteric layer 16 r asdescribed above (cholesteric reflecting layer forming step).

As in the case of the above-described example, the order of formation ofthe left circularly polarized light cholesteric layer 16 l and the rightcircularly polarized light cholesteric layer 16 r may be reversed.

Next, the sensor main body 12 and the substrate 42 are aligned,laminated, and bonded such that the planarizing layer 26 (bonding layer)and the right circularly polarized light cholesteric layer 16 r faceeach other (bonding step). As a result, the image sensor 40 shown inFIG. 4 is prepared.

It is preferable that the bonding is performed such that a gap betweenthe absorbing color filter 14 and the cholesteric reflecting layer 16 is100 μm or less. As a result, the occurrence of ghosting in which lighthaving transmitted through the respective color filters of the absorbingcolor filter 14 is incident on the solid image pickup element adjacentto the filter due to internal reflection or the like instead of beingincident on the solid image pickup element 12 a immediately below thefilter can be suppressed.

Further, the image sensor 20 shown in FIG. 2 may be prepared by removingthe substrate 42 from the image sensor 40 shown in FIG. 4 (removingstep). In this case, the image sensor 40 shown in FIG. 4 is anintermediate of the image sensor 20 shown in FIG. 2.

In addition, in the embodiment of the present invention, theconfiguration of the image sensor 50 shown in FIG. 5 that is prepared byforming the infrared absorbing layer 34 and the antireflection layer 36shown in FIG. 3 on the substrate 42 of the image sensor 40 shown in FIG.4 can also be used.

In the example shown in FIGS. 4 and 5, only one of the infraredabsorbing layer 34 and the antireflection layer 36 may be provided.

Hereinabove, the color filter, the image sensor, and the method ofmanufacturing a color filter according to the embodiment of the presentinvention have been described in detail. However, the present inventionis not limited to the above-described examples, and various improvementsand modifications can be made within a range not departing from thescope of the present invention.

The color filter and the image sensor according to the embodiment of thepresent invention can be suitably used in an imaging device such as adigital camera or a smartphone.

EXAMPLES

Hereinafter, the present invention will be described in more detailusing specific examples according to the present invention.

[Preparation of Cholesteric Reflecting Layer]

In order to verify whether or not desired spectral characteristics canbe realized in the color filter for an image sensor according to theembodiment of the present invention, a cholesteric reflecting layer wasprepared on a glass substrate to evaluate spectral characteristics. Inorder to measure an optical spectrum, a spectrophotometer UV-3100PC(manufactured by Shimadzu Corporation) was used.

<Preparation of Coating solution (R1)>

A compound (9), a compound (11), a dextrorotatory chiral agent 1, afluorine horizontal alignment agent 1, a polymerization initiator, and asolvent were mixed with each other to prepare a coating solution (R1)having the following composition. The compound (9) and the compound (11)correspond to the compound (9) and the compound (11) described above asthe examples of the polymerizable liquid crystal compound, and X¹ in thecompounds (11) represents 2.

<<Coating Solution (R1)>>

-   -   Compound (9): 80 parts by mass    -   Compound (11): 20 parts by mass    -   Dextrorotatory chiral agent 1: 3.76 parts by mass    -   Fluorine horizontal alignment agent 1: 0.1 part by mass    -   Polymerization initiator (IRGACURE 819, manufactured by BASF        SE): 4 parts by mass    -   Solvent (chloroform): an amount in which the solute        concentration was 25 mass %

The dextrorotatory chiral agent 1 and the fluorine horizontal alignmentagent 1 are the following compounds.

<Preparation of Coating Solution (R2) to Coating Solution (R6)>

Coating solutions (R2) to (R6) were prepared to have the samecomposition as that of the coating solution (R1) except that theaddition amount of the dextrorotatory chiral agent 1 in the preparationof the coating solution (R1) was changed as shown in the followingtable.

<Preparation of Coating Solution (L1) to Coating Solution (L8)>

Coating solutions (L1) to (L8) were prepared to have the samecomposition as that of the coating solution (R1) except that thefollowing levorotatory chiral agent 1 was used instead of thedextrorotatory chiral agent 1 in the preparation of the coating solution(R1) and the addition amount of the levorotatory chiral agent 1 waschanged as shown in the following table.

<Preparation of Glass Substrate (P1) With Photo-Aligned Film>

A photo-aligned film-forming coating solution 1 was prepared withreference to the description of Example 3 of JP2012-155308A.

The prepared photo-aligned film-forming coating solution 1 was appliedto the glass substrate using a spin coating method. As a result, aphoto-aligned film-forming film 1 was formed. The obtained photo-alignedfilm-forming film 1 was irradiated with polarized ultraviolet light (300mJ/cm², 750 W extra high pressure mercury lamp was used) through a wiregrid polarizer. As a result, a glass substrate (P1) with thephoto-aligned film was formed.

<Preparation of Right Circularly Polarized Light Cholesteric Layer(RF1)>

The coating solution (R1) was applied to the glass substrate (P1) withthe photo-aligned film using a spin coating method, was dried, and wasimmobilized. As a result, a coating film having a thickness of 5 μm wasformed.

The glass substrate (P1) with the photo-aligned film on which thecoating film of the coating solution (R1) was formed was heated on a hotplate at 80° C. for 1 minute such that the solvent was dried and removedand a cholesteric aligned state was formed. Next, using EXECURE 3000-W(manufactured by HOYA-SCHOTT), the glass substrate (P1) with thephoto-aligned film was irradiated with ultraviolet (UV) light for 10seconds at an illuminance of 30 mW/cm² at room temperature in a nitrogenatmosphere such that the alignment was immobilized. As a result, a rightcircularly polarized light cholesteric layer (RF1) was prepared.

A reflection center wavelength of the right circularly polarized lightcholesteric layer (RF1) was 728 nm in case of being measured using aspectrophotometer (spectrophotometer UV-3100PC, manufactured by ShimadzuCorporation). In other words, the reflection center wavelength is acenter wavelength of selective reflection.

<Preparation of Right Circularly Polarized Light Cholesteric Layer (RF2)to Right Circularly Polarized Light Cholesteric Layer (RF6)>

Right circularly polarized light cholesteric layer (RF2) to rightcircularly polarized light cholesteric layer (RF6) were prepared underthe same conditions as those of the right circularly polarized lightcholesteric layer (RF1), except that the coating solution (R2) to thecoating solution (R6) were used instead of the coating solution (R1) inthe step of preparing the right circularly polarized light cholestericlayer (RF1).

In addition, the reflection center wavelength of each of the rightcircularly polarized light cholesteric layers was measured under thesame conditions as those of the right circularly polarized lightcholesteric layer (RF1). The reflection center wavelength of each of theright circularly polarized light cholesteric layers was as shown in thefollowing table.

<Preparation of Left Circularly Polarized Light Cholesteric Layer (LF1)to Left Circularly Polarized Light Cholesteric Layer (LF8)>

Left circularly polarized light cholesteric layer (LF1) to leftcircularly polarized light cholesteric layer (LF8) were prepared underthe same conditions as those of the right circularly polarized lightcholesteric layer (RF1), except that the coating solution (L1) to thecoating solution (L8) were used instead of the coating solution (R1) inthe step of preparing the right circularly polarized light cholestericlayer (RF1).

In addition, the reflection center wavelength of each of the leftcircularly polarized light cholesteric layers was measured under thesame conditions as those of the right circularly polarized lightcholesteric layer (RF1). The reflection center wavelength of each of theleft circularly polarized light cholesteric layers was as shown in thefollowing table.

TABLE 1 Coating Reflection Center Solution Chiral Agent Addition AmountWavelength R1 Dextrorotatory 3.76 parts by mass 728 nm R2 Chiral Agent 13.47 parts by mass 786 nm R3 3.19 parts by mass 841 nm R4 2.95 parts bymass 918 nm R5 2.74 parts by mass 1013 nm R6 2.54 parts by mass 1049 nmL1 Levorotatory 6.27 parts by mass 723 nm L2 Chiral Agent 1 5.72 partsby mass 790 nm L3 5.42 parts by mass 847 nm L4 5.20 parts by mass 866 nmL5 4.87 parts by mass 911 nm L6 4.65 parts by mass 972 nm L7 4.38 partsby mass 1026 nm L8 4.11 parts by mass 1087 nm

[Preparation of Laminated Cholesteric Reflecting Layer (CF1)]

Chloroform was applied to the prepared right circularly polarized lightcholesteric layer (RF1) using a spin coating method, was heated on a hotplate at 80° C. for 1 minute, and a bashing treatment was performedthereon.

The coating solution (R2) was applied to the right circularly polarizedlight cholesteric layer (RF1) having undergone the bashing treatmentusing a spin coating method, was dried, and immobilized such that acoating film of the coating solution (R2) having a thickness of 5 μm wasformed. Accordingly, the total thickness of the laminate including theright circularly polarized light cholesteric layer (RF1) was 10 μm.

The right circularly polarized light cholesteric layer (RF1) on whichthe coating film of the coating solution (R2) was formed was heated on ahot plate at 80° C. for 1 minute such that the solvent was dried andremoved and a cholesteric aligned state was formed. Next, using EXECURE3000-W (manufactured by HOYA-SCHOTT), the right circularly polarizedlight cholesteric layer (RF1) was irradiated UV light for 10 seconds atan illuminance of 30 mW/cm² at room temperature in a nitrogen atmospheresuch that the alignment was immobilized. As a result, the rightcircularly polarized light cholesteric layer (RF2) was laminated on theright circularly polarized light cholesteric layer (RF1).

Hereinafter, the right circularly polarized light cholesteric layer(RF3) to the right circularly polarized light cholesteric layer (RF6)and the left circularly polarized light cholesteric layer (LF1) to theleft circularly polarized light cholesteric layer (LF8) weresequentially laminated under the same conditions using the coatingsolution (R3) to the coating solution (R6) and the coating solution (L1)to the coating solution (L8), respectively. As a result, the laminatedcholesteric reflecting layer (CF1) was prepared. The thickness of theprepared laminated cholesteric reflecting layer (CF 1) was 70 μm.

Regarding the prepared laminated cholesteric reflecting layer (CF1), atransmittance of light in a wavelength range of 700 to 1000 nm wasmeasured using a spectrophotometer (spectrophotometer UV-3100PC,manufactured by Shimadzu Corporation). As a result, the maximumtransmittance of light in a wavelength of 700 to 1000 nm was 5%.

[Preparation of Laminated Cholesteric Reflecting Layer (CF2)]

A laminated cholesteric reflecting layer (CF2) was prepared under thesame conditions as those of the laminated cholesteric reflecting layer(CF1), except that the two right circularly polarized light cholestericlayers (RF1) to the two right circularly polarized light cholestericlayer (RF6) and the two left circularly polarized light cholestericlayers (LF1) to the two left circularly polarized light cholestericlayers (LF8) were laminated in the step of preparing the laminatedcholesteric reflecting layer (CF1). The thickness of the preparedlaminated cholesteric reflecting layer (CF2) was 140 μm.

Regarding the prepared laminated cholesteric reflecting layer (CF2), themaximum transmittance of light in a wavelength range of 700 to 1000 nmwas 1% in case of being measured under the same conditions as those ofthe laminated cholesteric reflecting layer (CF1).

[Preparation of Image Sensor 1]

A red filter (R), a green filter (G), and a blue filter (B) as absorbingcolor filters corresponding to respective solid image pickup elementswere formed on a commercially available image sensor array using awell-known method, and a microlens was further laminated.

The laminated cholesteric reflecting layer (CF1) prepared as describedabove was bonded to the laminate using an adhesive such that thecholesteric layer faced the microlens side. As a result, an image sensor1 was prepared. A gap between the absorbing color filter and thecholesteric layer was 100 μm or less.

That is, the image sensor 1 according to this example has the sameconfiguration as the image sensor shown in FIG. 2, and the adhesivefunctions as a planarizing layer.

[Preparation of Image Sensor 2]

A red filter (R), a green filter (G), and a blue filter (B) as absorbingcolor filters corresponding to respective solid image pickup elementswere formed on a commercially available image sensor array using awell-known method, and a microlens and a planarizing layer were furtherlaminated.

A photo-aligned film was formed on the planarizing layer of the laminateunder the same conditions as those of the glass substrate (P1) with thephoto-aligned film.

The laminated cholesteric reflecting layer (CF2) was directly formed onthe photo-aligned film using the above-described method. As a result, animage sensor 2 was prepared. A gap between the absorbing color filterand the cholesteric layer was 100 μm or less.

That is, the image sensor 2 according to this example also has the sameconfiguration as the image sensor shown in FIG. 2.

EXPLANATION OF REFERENCES

-   10, 20, 30, 40: image sensor-   12: sensor main body-   12 a: solid image pickup element-   14: color filter-   14R: red filter-   14G: green filter-   14B: blue filter-   16: cholesteric reflecting layer-   16 r: right circularly polarized light cholesteric layer-   16 l: left circularly polarized light cholesteric layer-   24: microlens-   26: planarizing layer (bonding layer)-   32: aligned cholesteric layer-   34: infrared absorbing layer-   36: antireflection layer-   42: substrate

What is claimed is:
 1. A color filter for an image sensor comprising:two or more absorbing color filters that absorb light components havingdifferent wavelength ranges; a cholesteric reflecting layer in which aright circularly polarized light cholesteric layer having rightcircularly polarized light reflecting properties and a left circularlypolarized light cholesteric layer having left circularly polarized lightreflecting properties are laminated; and a microlens provided betweenthe absorbing color filters and the cholesteric reflecting layer;wherein a gap between the absorbing color filters and the cholestericreflecting layer is 100 μm or less.
 2. The color filter for an imagesensor according to claim 1, wherein a planarizing layer that covers themicrolens to planarize a surface of the microlens is provided betweenthe microlens and the cholesteric layer.
 3. The color filter for animage sensor according to claim 1, further comprising: a near infraredabsorbing layer having absorption properties in a near infrared range.4. The color filter for an image sensor according to claim 1, wherein anantireflection layer is provided at an interface in contact with air. 5.The color filter for an image sensor according to claim 1, wherein analigned cholesteric layer is provided at an interface in contact withthe cholesteric reflecting layer.
 6. The color filter for an imagesensor according to claim 5, wherein the aligned cholesteric layer is aphoto-aligned film.
 7. The color filter for an image sensor according toclaim 1, wherein in a plane of the right circularly polarized lightcholesteric layer and the left circularly polarized light cholestericlayer of the cholesteric reflecting layer, a plurality of reflectingregions that reflect light components having different wavelength rangesare provided, and reflecting regions that reflect light componentshaving the same wavelength range are laminated at the same position in aplane direction.
 8. The color filter for an image sensor according toclaim 1, wherein the right circularly polarized light cholesteric layerand the left circularly polarized light cholesteric layer of thecholesteric reflecting layer are formed by curing a polymerizablecholesteric liquid crystal composition.
 9. The color filter for an imagesensor according to claim 8, wherein the polymerizable cholestericliquid crystal composition includes at least one polymerizable liquidcrystal having a refractive index anisotropy Δn of 0.2 or higher, atleast one chiral agent that induces right or left twisting, and apolymerization initiator.
 10. The color filter for an image sensoraccording to claim 1, wherein a substrate is provided on a surface ofthe cholesteric reflecting layer opposite to the absorbing colorfilters.
 11. An image sensor comprising: the color filter for an imagesensor according to claim 1; and a sensor including solid image pickupelements that are arranged in a two-dimensional matrix.
 12. A method ofmanufacturing a color filter for an image sensor, the method comprising:a filter forming step of forming two or more absorbing color filtersthat absorb light components having different wavelength ranges on asensor including solid image pickup elements that are arranged in atwo-dimensional matrix; after the filter forming step, a microlensforming step of forming a microlens corresponding to a pixel of thesolid image pickup elements; and a cholesteric reflecting layer formingstep of forming a cholesteric reflecting layer in which a rightcircularly polarized light cholesteric layer having right circularlypolarized light reflecting properties and a left circularly polarizedlight cholesteric layer having left circularly polarized lightreflecting properties are laminated, the cholesteric reflecting layerforming step including a step of forming the right circularly polarizedlight cholesteric layer and a step of forming the left circularlypolarized light cholesteric layer, wherein in the cholesteric reflectinglayer forming step, the cholesteric reflecting layer is formed such thata distance between the absorbing color filters and the cholestericreflecting layer is 100 μm or less.
 13. The method of manufacturing acolor filter for an image sensor according to claim 12, wherein aplanarizing layer forming step of forming a planarizing layer thatcovers the microlens to planarize a surface of the microlens areprovided after the microlens forming step.
 14. The method ofmanufacturing a color filter for an image sensor according to claim 12,wherein the step of forming the right circularly polarized lightcholesteric layer in the cholesteric reflecting layer forming stepincludes a step of applying a polymerizable cholesteric liquid crystalcomposition including a chiral agent that induces right twisting, a stepof heating the polymerizable cholesteric liquid crystal composition toform a cholesteric liquid crystalline phase having right circularlypolarized light reflecting properties, and a step of exposing thecholesteric liquid crystalline phase to ultraviolet light to immobilizethe cholesteric liquid crystalline phase, and the step of forming theleft circularly polarized light cholesteric layer in the cholestericreflecting layer forming step includes a step of applying apolymerizable cholesteric liquid crystal composition including a chiralagent that induces left twisting, a step of heating the polymerizablecholesteric liquid crystal composition to form a cholesteric liquidcrystalline phase having left circularly polarized light reflectingproperties, and a step of exposing the cholesteric liquid crystallinephase to ultraviolet light to immobilize the cholesteric liquidcrystalline phase.
 15. The method of manufacturing a color filter for animage sensor according to any one of claim 12, further comprising: analigned layer forming step of forming an aligned cholesteric layer on asurface on which the cholesteric reflecting layer is to be formed. 16.The method of manufacturing a color filter for an image sensor accordingto claim 12, wherein an antireflection layer forming step of forming anantireflection layer is provided after the cholesteric reflecting layerforming step.
 17. The method of manufacturing a color filter for animage sensor according to claim 12, wherein an infrared absorbing layerforming step of forming a near infrared absorbing layer havingabsorption properties in a near infrared range is provided after thefilter forming step.
 18. The method of manufacturing a color filter foran image sensor according to claim 12, wherein before at least oneforming step among the respective forming steps, at least one treatmentstep among a bashing treatment step of performing a bashing treatment ona surface on which the forming step is to be performed using an organicsolvent, a plasma treatment step of performing a plasma treatment on asurface on which the forming step is to be performed, and asaponification treatment step of performing a saponification treatmenton a surface on which the forming step is to be performed using analkaline solution is performed.
 19. A method of manufacturing a colorfilter for an image sensor, the method comprising: a filter forming stepof forming two or more absorbing color filters that absorb lightcomponents having different wavelength ranges on a sensor includingsolid image pickup elements that are arranged in a two-dimensionalmatrix; after the filter forming step, a microlens forming step offorming a microlens corresponding to a pixel of the solid image pickupelements; and a cholesteric reflecting layer forming step of forming acholesteric reflecting layer in which a right circularly polarized lightcholesteric layer having right circularly polarized light reflectingproperties and a left circularly polarized light cholesteric layerhaving left circularly polarized light reflecting properties arelaminated on one surface of a substrate; and a bonding step oflaminating and bonding the sensor and the substrate to each other suchthat the absorbing color filters and the cholesteric reflecting layerface each other, wherein in the bonding step, the solid image pickupelement and the substrate are bonded to each other such that a distancebetween the cholesteric reflecting layer and the absorbing color filtersis 100 μm or less.
 20. The method of manufacturing a color filter for animage sensor according to claim 19, wherein a removing step of removingthe substrate is provided after the bonding step.